The present invention is a method for grinding silicon metalloid comprising grinding silicon metalloid in the presence of an effective amount of a grinding aid selected from the group consisting of carboxylic acids comprising at least 8 carbon atoms, alkali metal salts of carboxylic acids comprising at least 8 carbon atoms, and polydiorganosiloxanes.
Silicon metalloid (herein in the alternative referred to as "silicon") is a key raw material in organohalosilanes produced commercially in the fluidized-bed process often referred to as the Direct Process. In the Direct Process for producing alkylhalosilanes, an alkylhalide is reacted with particulate silicon in the presence of a catalyst comprising copper. It has long been recognized that in the Direct Process the size of the particulate silicon is important in determining the efficiency of the reaction of alkyl halides with silicon to form alkylhalosilanes. The efficiency of the reaction of alkyl halides with silicon is determined based on the amount of silicon charge that is converted to diakyldihalosilane and this conversion is in part dependent on the silicon particle size.
Windle, U.S. Pat. No. 3,604,634, describes a method of grinding calcium carbonate minerals comprising the steps of (a) forming an aqueous suspension comprising at least 25 percent by weight of the calcium carbonate mineral, and (b) grinding the aqueous suspension of calcium carbonate mineral with a particulate grinding material such as silica sand, calcined clay, flint granules, ceramic and glass beads.
Manfroy et al., U.S. Pat. Nos. 4,162,044 and 4,274,599, describe a process for grinding coal or ores containing metal values comprising carrying out the grinding in a liquid medium and with a grinding aid comprising an anionic polyelectrolyte derived from polyacrylic acid and dispersible in the liquid medium, the grinding aid being present in an amount effective to provide increased grinding efficiency.
Klimpel et al., U.S. Pat. No. 5,131,600, describe a process for the wet grinding of silica or siliceous gangue-containing solids comprising carrying out the grinding operation in the presence of liquid medium and at least one alkanol amine dispersible in the liquid medium.
Freeburne et al., U.S. Pat. No. 5,312,948, teach a process for the reaction of an alkyl halide with particulate silicon in a fluidized-bed process, where the particle size of the silicon is within a range of one micron to 85 microns.
The present invention provides a method for grinding silicon in the presence of an effective amount of a grinding aid selected from the group consisting of carboxylic acids comprising at least 8 carbon atoms, alkali metal salts of carboxylic acids comprising at least 8 carbon atoms and polydiorganosiloxanes to increase mill capacity, increase silicon grinding rate, increase silicon flowability, decrease silicon agglomeration and to narrow silicon particle size distribution.